OLEDs are becoming widely used in display and illumination devices. An OLED device is usually constructed on a transparent glass or plastic substrate, onto which a first electrode layer is deposited. This first electrode, which is usually the anode, is often applied using a sputtering process. The first electrode is usually transparent and can be made of a material such as aluminium doped zinc oxide (ZnO), tin-doped indium oxide (ITO) or a highly ductile transparent conductive polymer such as Poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) PEDOT:PSS, etc. Additional metal areas can be applied along the edges of the device, which metal areas will later be used as contact pads for the anode and the cathode. Once the first electrode layer has been applied, one or more layers of organic semiconductor materials, chosen for their light-emitting properties, are applied to give an active light-emitting layer. On top of this, a second electrode layer, usually the cathode, is applied such that an electrical contact is made between the second electrode and a contact pads on the edge of the OLED device. In a final step, the device is hermetically sealed to protect the device layers from moisture, and the anode and cathode are accessed only by the contact pads usually located on the outside edges of the device.
If it is desired that the OLED device should only emit light within certain areas instead of over the entire surface of the device, a shadow mask can be used to apply the second electrode. The shadow mask will have openings corresponding to the areas that are to emit light. However, using the established manufacturing techniques, only certain geometrical shapes can be realised for the light-emitting areas since each cathode area must be electrically connected to a contact pad or ‘patch’ outside the OLED encapsulation. This means that only very limited geometrical shapes can effectively be realised for the light emitting areas. To obtain other shapes, separate OLED elements, each of which has a second electrode realised to with a partial shape, could be combined to obtain an OLED with the overall desired light-emitting shape, but this approach is also less than satisfactory since the necessary encapsulation of each OLED element results in a clearly visible ‘seam’ between the separate elements.
Therefore, it is an object of the invention to provide a more economical way of obtaining an OLED device with separate light-emitting areas.